Police are treating the deaths of a family of four as a murder-suicide, as neighbours and friends say the Colombian parents struggled with their two autistic children.

The children Elisa, 11 and Martin, 10, were found dead in the home with their mother Maria Lutz, 43 and father Fernando Manrique, 44, on Monday after the school raised the alarm when the children and Ms Lutz failed to arrive.

Both of the children were deaf and autistic and described by the school as artistic.

Maria Claudia Lutz with Elisa, 11, and Martin, 10. The three plus father Fernando Manrique, 44 and the family dog were found dead at a New South Wales home on Monday.

When police visited the home in Davidson, in Sydney's north, they were confronted by the horrifying scene, which included the family's dead dog.

News Corp is reporting that none of the bodies showed signs of violence, and were found in separate locations in the house.

There is no word yet on whether the dead were all from the same family.

Police said a crime scene has been established and "will be examined by forensic officers".

Superintendent Dave Darcy of the Northern Beaches Local Area Command said the family were not known to police.

He said it was a tragic and horrific incident.

"It's extremely confronting, the officers -- we consistently have these concern for welfare cases and unfortunately in some cases, this is what the police are confronted with.

"Two young children have died, two adults have died, I just want to keep this investigation … untainted so our investigators can clearly and concisely get the information they need to come to the truth of what's happened.

"The mother in particular is held in very high regard in the community.

"Since coming to Australia they've made a significant contribution to how we live, they've done a fantastic job."

Police were now seeking to make contact with the family's next of kin.

A man, woman and two children plus a dog have been found dead at the home in Sydney&#39;s north.